1. Field of the Invention
In general, the present invention relates to circuits that reduce distortion and noise from signals that are amplified or are otherwise subject to distortion. More particularly, the present invention relates to circuits that correct a signal for distortion prior to the occurrence of the distortion.
2. Prior Art Description
Many modern electronic devices have circuitry that utilizes semiconductor devices, such as diodes and transistors. Such semiconductor devices are nonlinear in nature. That is, such devices have exponential characteristics that tend to produce signal distortions.
Circuit designers are aware of the distortions created by such semiconductor devices. Consequently, circuit designers actively attempt to create circuits that minimize the inherent distortions. However, this typically requires circuit designers to create circuits with semiconductor devices that are forward biased, i.e. consuming power. The results are circuit designs that are highly complex and/or consume excess amounts of power, just to obtain an acceptable level of distortion.
For example in U.S. Pat. No. 7,680,468 entitled, Method and Apparatus For Distortion Correction Of RF Amplifiers, a circuit is presented for reducing the distortion in an amplified signal. However, the circuit is complex, using a digital signal processor, a local oscillator and band pass filters. Furthermore, the circuit is only suitable for a small band of signal frequencies. The prior art circuit is also limited in that it cannot work with direct current signals.
Even simpler correction circuits, such as that disclosed in U.S. Pat. No. 6,606,484 to Faulkner, entitled Distortion Correction Circuit For Direct Conversion Receiver, also require a local oscillator and band pass filtering. Accordingly, such prior art correction circuits cannot operate with DC input signals.
A need therefore exists for a circuit and method that can reduce distortion and noise in a wide range of signals, that include both AC and DC signals. A need also exists for a circuit and method that can reduce distortion yet embodies simple analog computing circuitry, therein allowing the correction circuit to be simply integrated into other circuit designs. Lastly, a need exists for a distortion correction circuit that consumes very little power and does not contain any semiconductor devices that must be forward biased in order for the circuit to operate properly. These needs are met by the present invention as described and claimed below.